Fixed creation of new image

Removed creation of template from url/uploaded file from base image model.
Created DownloadService for downloading files from url.
Replaced import_from_xml by DownloadService in existing code

There is still an obsolete import_xml_from_url method in
app/util/deployable_xml.rb which is apparently used only in tests.
This will be removed in separate patch because it fix is not
straightforward.
Bumped deltacloud-client version to 1.0.4

We had quite old 0.5.0 version of deltacloud-client in Gemfile.lock.
This version doesn't play nicely with openstack provider - it's not
possible to add openstack provider account because x-deltacloud-provider
header is not sent properly. There is also newer version 1.0.5 now, but
bumping to 1.0.4 which I know is in Fedora.